The present invention broadly relates to the recovery of metal ions from ionic solutions. More specifically, the present invention relates to electrowinning cells for use in recovering metal ions from aqueous solutions as elementary metals. In particular, the present invention is directed to an improved electrowinning system, method and apparatus.
Electrowinning cells are mechanisms used extensively for recovering metal ions from solutions as elementary metals. Such cells may be used, for example, in the recovery and purification of copper. The mechanism generally consists of a collection tank, an anode, a cathode and a direct current (DC) power source. The metals gain electrons, achieve a valence of zero and deposit on the cathode.
The efficiency of an electrowinning cell is directly proportional to the concentration of the metal ions in the immediate vicinity of the cathode. As metal ions deposit on the cathode as their elementary metals during the electrowinning process, however, the concentration of metal ions in the vicinity of the cathode decreases, thereby reducing the efficiency of the cell.
In order to improve the efficiency of an electrowinning cell, it is known to constantly agitate or move the ionic solutions by various mechanisms, such as by the use of fluidized beds of glass beads, rotating cathodes, and other means. These mechanisms, however, cannot significantly increase efficiency in the later stage of electrowinning when most of the metal has been recovered on the cathode and the concentration of metal ions in the solution is much lower than optimum levels.
Accordingly, this dilute solution is typically discharged from the cell and the metal ions are treated with secondary methods to concentrate the metal ions in solution again. One such method is to adjust the pH of the solution to between 4 and 6, and treat the water with a chelating type of ion exchange resin. The regenerant from the resin is then sent back to the electrowinning cell. Such a method of concentrating requires decanting the cell, adding chemicals for pH adjustment, and regenerating the solution from the ion exchange resin. The use of such secondary methods of concentration interrupts the electrowinning process and impacts the overall efficiency of the cell.
Accordingly, there remains a need to provide a new and improved electrowinning cell apparatus and system and a new and improved method of concentrating an ionic solution for use with an electrowinning cell. The present invention is directed to meeting these needs.
It is an object of the present invention to provide an efficient electrowinning cell adapted to recover metal ions from a solution.
It is another object to provide a cost effective and efficient method of concentrating metal ions in a solution for use in an electrochemical cell.
It is yet another object to provide a method and apparatus for improving the efficiency of an electrowinning cell which avoids interrupting the electrochemical process.
It is still a further object to provide an electrowinning cell which improves the efficiency of standard electrowinning cells in the later stages of electrowinning.
It is yet another object to provide a new and improved system for reducing metal ions in a solution to their corresponding elementary metals.
Yet another object is to provide an efficient and integrated electrowinning cell system.
A still further object is to provide an improvement to an electrowinning cell which circumvents the necessity for performing traditional secondary methods of concentrating metal ions in an electrowinning solution.
According to the present invention, an electrowinning cell is provided which is adapted to recover metal ions from a solution as their corresponding elementary metals. The electrowinning cell comprises a reservoir adapted to receive a solution containing metal ions at a selected concentration, an anode and a cathode disposed in the reservoir, a filter in fluid communication with the reservoir and operative to receive the solution from a location proximate to the cathode, and a return means operative to return the first portion of the solution to the reservoir. The anode and cathode are operative to establish an electric potential difference therebetween. The filter is operative to retain a first portion of the solution having a first concentration of metal ions and to remove a second portion of the solution having a second concentration of metal ions lower than the first concentration, thereby to improve the concentration of metal ions in the solution and consequently increase the efficiency of the electrowinning cell. The filter according to the present invention is preferably a nanofilter, and more preferably a nanofilter of the crossflow membrane type.
It is preferred that the electrowinning cell according to the present invention includes a solution holding tank in fluid communication with the reservoir and the filter. A filter collection tank is also preferred, where the filter collection tank is in fluid communication with the solution holding tank and the filter. A microfilter may be disposed between the nanofilter and the filter collection tank, in order to filter out undesired particles and the like which may otherwise obstruct the nanofilter. The electrowinning cell also preferably includes an electrowinning collection tank in fluid communication with the solution holding tank and the reservoir. At least one pump may be provided to circulate the solution between the components of the apparatus.
A flow-rate sensor and a valve in fluid communication with the solution may be provided. The valve has a first state allowing fluid flow and a second state preventing fluid flow. A microprocessor control may further be provided which is operative to receive data from the flow-rate sensor and to adjust the flow-rate of the solution by moving the valve between the first and second states.
The present invention is also directed to a method of concentrating metal ions in a solution for use in an electrochemical cell. The method comprises the steps of drawing a portion of a solution containing metal ions from a region proximate to a cathode in an electrochemical cell, filtering the portion of the solution thereby to create a retentate having a first concentration of metal ions and a permeate having a second concentration of metal ions lower than the first concentration, and returning the retentate to the electrochemical cell.
A system for reducing metal ions in a solution to their corresponding elementary metals is also provided. The system comprises a fluid source operative to provide a solution containing metal ions at a selected concentration, a reservoir in fluid communication with the fluid source and operative to receive the solution, an anode and a cathode each disposed in the reservoir, and a power source operative to supply electric current to the anode and the cathode. A filter in fluid communication with the reservoir includes a membrane, wherein the filter has a first region on one side of the membrane and a second region on an opposite side of the membrane. A retentate of the solution is disposed in the first region of the filter, and a permeate of the solution is disposed in the second region of the filter. The retentate has a first concentration of metal ions and the permeate has a second concentration of metal ions lower than the first concentration. A return means is operative to return the retentate to the reservoir.
The present invention also provides an improvement to an electrowinning cell operative to reduce metal ions at a selected concentration in a solution at a location proximate to a cathode in a reservoir to their corresponding elementary metals. The improvement comprises a filter apparatus in fluid communication with the reservoir and operative to draw the solution from a region proximate to the cathode and to filter the solution into a first portion having a first concentration of metal ions greater than the selected concentration and a second portion having a second concentration of metal ions lower than the selected concentration. The filter apparatus is further operative to return the first portion to the reservoir. The filter apparatus may include a filter, a valve, a conduit and a pump, and the filter may include a membrane filter of the nanofiltration range.
These and other objects of the present invention will become more readily appreciated and understood from a consideration of the following detailed description of the exemplary embodiment of the present invention when taken together with the accompanying drawings, in which: